A coop bundle is an bundle of games from different devs, splitting revenue and gaining from each other fanbase, it helps each participant to gain an extra little perk of getting known, the more games, the better!
If you want to join I suggest you joining my discord server here https://discord.gg/8KsmHtQ
I'll try to get in contact with as many devs as possible, you can contact some others too, maybe mention my name bc I've built up a decent little fanbase, we want mainly RPGs but really any other game works, maybe something spooky for Halloween would be great, we will discuss specific details on my server! (game has to be paid!)
As of writing this, I already got one other person who wants to join!